doc: update cli flag in crypto.md

PR-URL: #20400
Fixes: #20385
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Shigeki Ohtsu <ohtsu@ohtsu.org>

doc/api/crypto.md

@@ -1561,7 +1561,8 @@ behavior.
 
 The `algorithm` is dependent on the available algorithms supported by the
 version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc.
-On recent releases of OpenSSL, `openssl list-message-digest-algorithms` will
+On recent releases of OpenSSL, `openssl list -digest-algorithms`
+(`openssl list-message-digest-algorithms` for older versions of OpenSSL) will
 display the available digest algorithms.
 
 Example: generating the sha256 sum of a file